Spin-valve magnetic head with the pinned layer having different directions for its magnetization axis and its easy axis

ABSTRACT

A spin-valve magnetic head has a first ferromagnetic layer with a first easy axis of magnetization extending in a first direction, and a second ferromagnetic layer provided on, and separated from, the first ferromagnetic layer. The second ferromagnetic layer has a magnetization in a second direction substantially perpendicular to the first direction. The magnetization defines a line in the second direction. An anti-ferromagnetic layer provided on the second ferromagnetic layer is exchange coupled to the second ferromagnetic layer. The second ferromagnetic layer has a second easy axis of magnetization extending in a direction intersecting the line in the second direction.

BACKGROUND OF THE INVENTION

The present invention generally relates to magnetic heads and moreparticularly to an improvement of a GMR (giant magneto-resistance) headhaving a so-called spin-valve structure.

A GMR head is a high-sensitivity magnetic head that detects a change ofresistance of a magnetic layer that in turn occurs in response to achange of direction of a very weak external magnetic field. Because ofthe high magnetic sensitivity, a GMR head is expected to play a majorrole in a high-density magnetic recording apparatus as a high-resolutionand high-sensitivity magnetic head.

FIG. 1 shows the overall construction of a magnetic head 10 having atypical conventional spin-valve structure, while FIG. 2 shows theconstruction of a spin-valve head 14 used in the magnetic head of FIG.1.

Referring to FIG. 1, the magnetic head 10 includes a lower magneticshield layer 12 of a magnetic material such as FeNi, CoFe or FeNprovided on a substrate 11 of Al₂ TiC. On the foregoing lower magneticshield layer 12, there is provided a spacer layer 13 of a non-magneticmaterial such as A1₂ O₃, and a magnetic sensor 14 having a spin-valvestructure is formed on the spacer layer 13.

The magnetic sensor 14 is covered by another spacer layer 15 also of anon-magnetic material similar to the spacer layer 13, and an uppermagnetic shield layer 16 of a soft magnetic material such as FeNi orCoFe is provided on the spacer layer 15. Thereby, the spacer layer 13,the magnetic sensor 14 and the spacer layer 15 form together a minutemagnetic read gap between the upper and lower magnetic shield layers 12and 16 with a size of about 200 nm.

On the upper magnetic shield layer 16, there is provided another spacerlayer 17 of a non-magnetic material with a thickness of about 350 nm,and a coil pattern 19 is provided on the spacer layer 17 with anintervening insulation layer 18, wherein the insulation layer 18continuously has a reducing thickness thereof toward a front end 10A ofthe magnetic head 10. The coil pattern 19 is covered by anotherinsulation layer 20, and a magnetic pole 21 of a magnetic material suchas FeNi or CoFe is provided on the foregoing another insulation layer 20such that the thickness of the insulation layer 20 decreasescontinuously toward the foregoing front end 10A of the magnetic head 10.As a result of the decreasing thickness of the insulation layers 18 and20 at the front end 10A of the magnetic head 10, the magnetic pole 21makes direct contact with the spacer layer 17 at the front end 10A.There, a minute magnetic write gap is formed between the upper magneticshield 16 and the magnetic pole 21. It should be noted that the uppermagnetic shield 16 extends to the magnetic pole 21 at a part notillustrated in FIG. 1, and a magnetic circuit is formed.

The magnetic head 10 scans the surface of a magnetic recording mediumsuch as a magnetic disk at the foregoing front edge surface 10A, and themagnetic sensor 14 detects the magnetization recorded on the surface ofthe magnetic recording medium at the foregoing magnetic read gap.Further, a recording of information is made on the magnetic recordingmedium at the foregoing write gap by energizing the coil 19 by aninformation signal.

FIG. 2 shows the construction of the magnetic sensor 14 in detail,wherein those parts explained already with reference to FIG. 1 aredesignated by the same reference numerals and the description thereofwill be omitted.

Referring to FIG. 2, the magnetic sensor 14 includes a magneticdetection layer or so-called "free layer" 14A of a soft magneticmaterial such as CoFe or NiFe formed on the spacer layer 14, wherein thefree layer changes the direction of magnetization freely in response tothe magnetization of the magnetic recording medium.

On the free layer 14A, there is provided an intermediate layer 14B of anon-magnetic material such as Cu, and a fixed magnetization layer orso-called "pinned layer" 14C is provided on the intermediate layer 14Bwith a predetermined fixed magnetization, wherein the pinned layer 14Cis formed of a soft magnetic material such as CoFe or NiFe similarly tothe free layer 14B. It should be noted that the magnetization of thepinned layer 14C is fixed in the direction of magnetization of amagnetization-fixing layer or so-called "pinning layer" 14D, wherein thepinning layer 14D is formed of an anti-ferromagnetic material such asFeMn or PdPtMn and provided on the pinned layer 14C. It should be notedthat the pinning layer 14D fixes the magnetization of the pinned layer14C by spin-exchange interaction. Thereby, the magnetization of themagnetic recording medium is detected by detecting a change of electricresistance that occurs in response to the change of direction ofmagnetization in the free layer 14A with respect to the direction ofmagnetization in the pinned layer 14c. In FIGS. 1 and 2, it should benoted that the electrodes for detecting the foregoing resistance changeis omitted from illustration. Further, it should be noted that thepinning layer 14D, lacking a spontaneous magnetization, is relativelyimmune to the external magnetic field.

In the magnetic sensor 14 having such a construction, in which thedirection of magnetization of the free layer 14A changes in response tothe direction of magnetization of the magnetic recording medium, itshould be noted that the resistance of the magnetic sensor 14 becomesminimum when the direction of magnetization of the layer 14A is parallelto the direction of the magnetization of the pinned layer 14C. When thedirection of magnetization of the layer 14A is in an anti-parallelrelationship with the direction of magnetization of the pinned layer14C, on the other hand, the resistance of the magnetic sensor 14 becomesmaximum.

In the case of using the magnetic sensor 14 for the magnetic head 10, itis advantageous to set the direction of magnetization of the pinnedlayer 14C perpendicular to the direction of magnetization of the freelayer 14A in a free state in which there is no external magnetic fieldapplied to the magnetic sensor 14. See FIG. 3A. By doing so, theresistance of the magnetic sensor 14 is increased or decreased generallysymmetrically depending on whether the magnetization of the magneticrecording medium is parallel or anti-parallel to the magnetization ofthe pinned layer 14C, as indicated in FIG. 3B. Such a generallysymmetric increase and decrease of the resistance facilitates the signalprocessing in the magnetic recording and reproducing apparatus.

It should be noted that the control of magnetization of a magnetic bodyis conducted in a heat treatment process.

FIG. 4 shows a heat treatment process conducted conventionally in theprocess of forming the spin-valve structure of FIG. 2.

Referring to FIG. 4, the spin valve structure of FIG. 2 is formed in astep 1 of FIG. 4 by depositing the layers 14A-14D under the existence ofan initial magnetic field with a predetermined initial directiondesignated as a 0° direction. The free layer 14A thus formed has an easyaxis of magnetization in the foregoing 0° direction.

Next, in the step 2 of FIG. 4, the spin-valve structure of FIG. 2 issubjected to a thermal annealing process to a temperature close to ablocking temperature of the pinning layer 14D, and a magnetic field isapplied in the foregoing 0° direction as indicated by blank arrows. As aresult, the direction of magnetization of the pinned layer 14C isaligned in the 0° direction.

FIGS. 5A and 5B explain the blocking temperature.

In a magnetic system in which an anti-ferromagnetic layer and a softmagnetic layer form an exchange coupling as in the case of thespin-valve structure of FIG. 2, it should be noted that the hysteresiscurve of the magnetic system is displaced along the horizontal axisrepresenting the magnetic field H by an amount Hua as indicated in FIG.5A as a result of the pinning of magnetization caused in the softmagnetic layer such as the pinned layer 14C by the anti-ferromagneticpinning layer 14D. This phenomenon means that it is insufficient in amagnetic system that includes such an anti-ferromagnetic layer, to applya magnetic field just enough to cause an inversion of magnetization inan ordinary magnetic system not including an anti-ferromagnetic layer,for causing an inversion of magnetization. In order to achieve this, itis necessary to increase the magnetization by an amount Hua. This is thepinning of magnetization.

FIG. 5B shows the temperature dependence of the quantity Hua.

Referring to FIG. 5B, it should be noted that the quantity Hua decreaseswith increasing temperature and reaches zero at a blocking temperatureT_(B). In other words, the magnetization of the spin valve structure ofFIG. 2 can be controlled as desired by an external magnetic field whenthe system is heated to a temperature close to or higher than theblocking temperature T_(B). The pinning of magnetization in such amagnetic system is eliminated when the system is heated to the blockingtemperature T_(B) or higher.

Referring back to FIG. 4, the pinned layer 14C is magnetized in theforegoing 0° direction as a result of the thermal annealing processconducted at the temperature close to the blocking temperature T_(B),and the anti-ferromagnetic pinning layer 14D forms an exchange couplingwith the pinned layer 14C. By cooling the structure thus formed to roomtemperature environment in the step 3 of FIG. 4, a structure in whichthe pinned layer 14C is magnetized in the 0° direction is obtained. Inthe structure of step 3 of FIG. 4, the magnetization of the pinned layer14C is pinned by the pinning layer 14D. As a result of the thermalannealing process in the step 2 of FIG. 4, the magnetic shield layers 12and 16 and the magnetic pole 21 forming the magnetic head 10 of FIG. 1are all magnetized in the foregoing 0° direction.

Next, in the step 4 of FIG. 4, the structure of step 3 of FIG. 4 isheated to a temperature close to the blocking temperature T_(B) again,and an external magnetic field is applied to the spin valve structure ina direction perpendicular to the foregoing 0° direction. As a result,the magnetization of the pinned layer 14C is rotated by 90°, and astructure shown in step 5 of FIG. 4 is obtained, in which it should benoted that the direction of magnetization of the pinned layer 14C isperpendicular to the direction of easy axis of magnetization of the freelayer 14A.

In the process of FIG. 4, however, there arises a problem, associatedwith the fact that the entire magnetic head 10 including the spin-valvemagnetic sensor 14 is heated to the temperature close to the blockingtemperature T_(B), in that the direction of magnetization of themagnetic shields 12 and 16 or the direction of magnetization of themagnetic pole 21, which has been initialized in the step 2, may bechanged unwantedly. Further, such thermal annealing and magnetizationprocesses conducted at the temperature close to the blocking temperaturemay cause a 90° rotation in the easy axis of magnetization from thedesired 0° direction as indicated by a broken arrow in step 5 of FIG. 4.When this occurs, the detection characteristic of the magnetic sensor 14is modified from the characteristic of FIG. 3B and the magnetic sensor14 would produce an asymmetric output in response to the magnetizationof the magnetic recording medium.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful magnetic head, a fabrication process thereof, and amagnetization control method of a magnetic film, wherein the foregoingproblems are eliminated.

Another and more specific object of the present invention is to providea magnetic head using a spin-valve magnetic sensor wherein the directionof easy axis of magnetization of a free layer is set perpendicular tothe direction of magnetization of a pinned layer.

Another object of the present invention is to provide a spin-valvemagnetic head, comprising:

a first ferromagnetic layer having a first easy axis of magnetizationextending in a first direction;

a second ferromagnetic layer provided on said first ferromagnetic layerwith a separation therefrom, said second ferromagnetic layer having amagnetization in a direction substantially perpendicular to said firsteasy axis of magnetization; and

an anti-ferromagnetic layer provided on said second ferromagnetic layerin exchange coupling therewith;

said second ferromagnetic layer having a second easy axis ofmagnetization extending in a direction intersecting said seconddirection.

Another object of the present invention is to provide a method offabricating a spin-valve magnetic head including a layered body of afirst ferromagnetic layer having a first easy axis of magnetizationextending in a first direction, a non-magnetic layer formed on saidfirst ferromagnetic layer, a second ferromagnetic layer provided on saidnon-magnetic layer, and an anti-ferromagnetic layer provided on saidsecond ferromagnetic layer in exchange coupling therewith, said methodcomprising:

a first thermal annealing process including the steps of: annealing saidlayered body in a first annealing state; and applying a magnetic fieldto said layered body in a second direction different from said firstdirection while maintaining said layered body in said first annealingstate; and

a second thermal annealing process including the steps of: annealingsaid layered body, after said first thermal annealing process, in asecond annealing state; and applying a magnetic field in a thirddirection different from said second direction while maintaining saidlayered body in said second annealing state.

Another object of the present invention is to provide a method offabricating a spin-valve magnetic head including a layered body of afirst ferromagnetic layer having a first easy axis of magnetizationextending in a first direction, a non-magnetic layer formed on saidfirst ferromagnetic layer, a second ferromagnetic layer provided on saidnon-magnetic layer, and an anti-ferromagnetic layer provided on saidsecond ferromagnetic layer in exchange coupling therewith, said methodcomprising the steps of:

annealing said layered body; and

applying a magnetic field to said layered body in a second directiondifferent from said first direction while annealing said layered body;

wherein said second direction intersects said first direction with anangle exceeding 90°.

Another object of the present invention is to provide a method ofmagnetizing a magnetic system including a ferromagnetic layer magnetizedin a first direction and an anti-ferromagnetic layer provided on saidferromagnetic layer in exchange coupling therewith, said methodcomprising:

a first thermal annealing process including the steps of: annealing saidmagnetic system in a first annealing state; and applying a magneticfield to said magnetic system in a second direction different from saidfirst direction while maintaining said magnetic system in said firstannealing state; and

a second thermal annealing process including the steps of: annealingsaid magnetic system, after said first thermal annealing process, to asecond annealing state; and applying a magnetic field in a thirddirection different from said second direction while maintaining saidmagnetic system in said second annealing state.

Another object of the present invention is to provide a method ofmagnetizing a magnetic system including a ferromagnetic layer magnetizedin a first direction and an anti-ferromagnetic layer provided on saidferromagnetic layer in exchange coupling therewith, said methodcomprising:

annealing said magnetic system; and

applying a magnetic field to said magnetic system in a second directiondifferent from said first direction while annealing said magneticsystem, to cause a rotation of magnetization in said ferromagnetic layerto a desired angle;

wherein said second direction intersects said first direction with anangle exceeding said desired angle.

According to the present invention, the annealing process for rotatingthe magnetization of the second ferromagnetic layer is conducted at alow temperature set such that no substantial rotation occurs in the easyaxis of magnetization of the first as well as second ferromagneticlayers. As the temperature used for the annealing process is set low assuch, the process of rotating the magnetization may be conducted inplural times by rotating the direction of the external magnetic fieldstepwise each time. In this case, it is particularly advantageous to setthe direction of the external magnetic field to a direction exactlyopposing the first direction in the final annealing process. Thereby,the easy axis of magnetization of the first ferromagnetic layer isaligned exactly to the first direction even when the direction of theeasy axis of magnetization is offset slightly as a result of theannealing processes. When the rotation of magnetization of the secondferromagnetic layer is to be conducted in a single step, on the otherhand, the direction of the external magnetic field is set with anexcessive, offset angle with respect to the desired direction ofmagnetization.

As a result of the low temperature heat treatment processes, othermagnetic members or parts of the magnetic head are not affected ordeteriorated even when the annealing is applied repeatedly for causingthe desired rotation of the magnetization, and the magnetic head shows anear-ideal resistance change as indicated in FIG. 3B. In the magnetichead of the present invention, the direction of magnetization of thesecond ferromagnetic layer does not coincide with the direction of theeasy axis of magnetization thereof.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction of a conventional magnetichead that uses a conventional spin-valve magnetic sensor;

FIG. 2 is a diagram showing the construction of a conventionalspin-valve magnetic sensor;

FIGS. 3A and 3B are diagrams showing the principle of an idealspin-valve magnetic sensor that changes a resistance value thereofsymmetrically with the direction of magnetization of a recording medium;

FIG. 4 is a diagram showing a conventional process of forming thespin-valve magnetic sensor of FIG. 2;

FIGS. 5A and 5B are diagrams explaining the blocking temperature;

FIG. 6 is a diagram showing the fundamental construction of thespin-valve magnetic sensor according to the present invention;

FIG. 7 is a diagram showing the fabrication process of a magnetic headaccording to a first embodiment of the present invention;

FIGS. 8A-8C are diagrams showing a rotation of magnetization or easyaxis of magnetization that occurs in a magnetic layer in the thermalannealing processes of FIG. 7;

FIG. 9 is a diagram showing the fabrication process of a magnetic headaccording to a second embodiment of the present invention; and

FIGS. 10A and 10B are diagrams showing a rotation of magnetizationoccurring in a magnetic layer in the thermal annealing processes of FIG.9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[FIRST EMBODIMENT]

FIG. 6 shows the construction of a spin-valve magnetic sensor 30according to a first embodiment of the present invention wherein thespin-valve magnetic sensor 30 is used in the magnetic head 10 of FIG. 1in place of the spin-valve magnetic sensor 14.

Referring to FIG. 6, the spin-valve magnetic sensor 30 includes a Tafilm 31 formed on the spacer layer 13 with a thickness of about 10 nm,and a NiFe film 32a is formed on the Ta film 31 with a thickness ofabout 2 nm. On the NiFe film 32a, there is provided a CoFe film 32b witha thickness of about 5.5 nm, wherein the films 32a and 32b form aferromagnetic free layer 32 corresponding to the free layer 14A of FIG.2.

In the structure of FIG. 6, a non-magnetic layer 33 of Cu is formed incorrespondence to the non-magnetic layer 14B of FIG. 2 with a thicknessabout 3.5 nm, and a pinned layer 34 of CoFe is formed on thenon-magnetic layer 33 in correspondence to the ferromagnetic pinnedlayer 14c of FIG. 2, with a thickness of about 3.5 nm. On the pinnedlayer 34, there is formed a pinning layer 35 of PdPtMn in correspondenceto the pinning layer 14D with a thickness of about 25 nm. The pinninglayer 35 is formed directly on the pinned layer 34 and establishes anexchange coupling with the layer 35. It should be noted that the pinninglayer 35 has a blocking temperature of about 300° C.

FIG. 7 shows the thermal annealing process conducted on the structure ofFIG. 6 according to a first embodiment of the present invention, whereinit should be noted that the thermal annealing process of FIG. 7 isconducted in a state that the spin-valve magnetic sensor 30 is attachedintegrally to the magnetic head 10.

Referring to FIG. 7, the structure of FIG. 2 is formed in the step 1while applying a predetermined magnetic field in a predetermineddirection, and the free layer 32 thus formed has the magnetization aswell as the easy axis of magnetization in the direction shown in thestep 1 with a solid arrow. This direction is defined as a "0°direction."

Next, in the step 2, the spin-valve sensor 30 is held in a d.c. magneticfield of 2.5 kOe and annealed at a temperature of about 250 ° C. forabout 3 hours. As a result of the thermal annealing process of the step2, the direction of magnetization and the direction of easy axis ofmagnetization are aligned in the 0° direction as indicated by a solidarrow in the step 3 of FIG. 7. The thermal annealing process of the step2 of FIG. 7 is conducted in a high vacuum environment in which thepressure is set to 1.5×10⁻⁵ Pa or lower. The state of the step 3 isdesignated as initial state. As a result of the thermal annealingprocess in the step 2, the magnetic shield layers 12 and 16 and furtherthe magnetic pole 21 are magnetized in the initial step 3 of FIG. 7 inthe foregoing 0° direction.

Next, in the step 4 of FIG. 7, the spin-valve magnetic sensor 30 isapplied with an external magnetic field acting perpendicularly to theforegoing 0° direction and a thermal annealing process is applied at atemperature of about 210° C. for about 2 hours. It should be noted thatthe temperature of 210° C. is substantially lower than the temperatureof 250° C. used in the thermal annealing process in the step 2 of FIG.7. In the thermal annealing process of the step 4, the magnitude of theexternal magnetic field is set identical to the case of the step 2, andthe thermal annealing process is conducted under the high vacuumenvironment of 1.5×10⁻⁵ Pa or lower in pressure.

FIG. 8A shows the change of direction of the magnetization in the pinnedlayer 34 for the case in which the temperature of the thermal annealingprocess is changed from 210° C. to 250° C. As already noted, theexternal magnetic field is applied in the direction substantiallyperpendicular to the initial magnetization direction similarly to thestep 4 of FIG. 7. In FIG. 8A, the duration of the thermal annealingprocess is set to 3 hours, which is slightly longer than the durationused in the step 4 of FIG. 7.

Referring to FIG. 8A, it can be seen that the magnetization of thepinned layer 34 causes a rotation of about 84°when the temperature ofthe thermal annealing process is set to 250° C. in the step 4 similarlyto the case of the step 2 of FIG. 7. However, the amount of rotation isdecreased to about 77° when the temperature of the thermal annealingprocess is reduced to about 230° C. Further, the amount of rotation isreduced to about 67°when the temperature of the thermal annealingprocess is reduced to about 210°, which is the temperature used in thestep 4 of FIG. 7.

This means that the full 90° rotation of the magnetization is notpossible in the low temperature thermal annealing process used in thestep 4 of FIG. 7, even when the duration of the thermal annealingprocess is continued for 3 hours or more, and the direction ofmagnetization of the pinned layer 34 obtained in the thermal annealingprocess of the step 4 forms an intermediate angle between the 0°direction and the 90° direction. Further, the free layer 32 may alsocause some rotation of magnetization as a result of the thermalannealing process in the step 4 of FIG. 7.

Thus, in the present invention, a step 6 shown in FIG. 7 is conductedafter the step 5, in which an external magnetic field acting in thesubstantially opposing direction (180°) to the foregoing 0° direction isapplied to the spin-valve magnetic sensor 30, and a thermal annealingprocess is conducted at a temperature of about 210° C. for 2 hours inthis state similarly to the thermal annealing process in the step 4 ofFIG. 7. As a result of the thermal annealing process of the step 6, themagnetization of the pinned layer 34 now extends in the directionperpendicular to the initial 0° direction as indicated in the step 7 ofFIG. 7. In the step 7, it should further be noted that, as a result ofthe thermal annealing process conducted under the existence of theexternal magnetic field acting in the 180° direction, the magnetizationof the free layer 32, which has been slightly offset from the 0°direction in the step 5, is once again aligned to the initial 0°direction.

FIG. 8B shows the rotation of the magnetization of the pinned layer 34occurring in each of the thermal annealing steps 2, 4 and 6 representedrespectively as A, B and C. As can be seen in FIG. 8B, the 90° rotationof the magnetization is successfully achieved by repeating the thermalannealing steps. In the point B corresponding to the step 4, it shouldbe noted that the amount of rotation is about 45°, which is smaller thanthe rotation angle of about 67° shown in FIG. 8A for the sametemperature. This discrepancy between these different rotational anglesis caused merely as a result of the difference in the duration of thethermal annealing process in the experiment of FIG. 8A and in theexperiment for FIG. 8B.

As already explained with reference to FIGS. 3A and 3B, the spin-valvemagnetic sensor 30 of the present embodiment increases or decreases theresistance depending on the direction of magnetization on a recordingmedium symmetrically.

FIG. 8C shows the rotation of the easy axis of magnetization of the freelayer 32 for the case in which the temperature of the thermal annealingprocess is changed in the step 4 of FIG. 7.

Referring to FIG. 8C, the easy axis of magnetization rotatessignificantly when the thermal annealing process of the step 4 isconducted at the conventional temperature of about 250° C. On the otherhand, the easy axis of magnetization rotates little when the thermalannealing process is conducted at the temperature of about 210° C. as inthe case of the present invention. Even if such a rotation occurred, themagnitude of the rotational angle is limited without 10°. The sameapplies also to the thermal annealing process conducted at 230° C.

In relation to the finding of FIG. 8C, it should be noted that thethermal annealing process at 210° C. does not cause a rotation of easyaxis of magnetization in the pinned layer 34 that has a compositionsubstantially identical to the composition of the free layer 32, asindicated by a broken line in the step 7 of FIG. 7. In other words, thespin valve magnetic 30 that has been applied with a low temperaturethermal annealing process for causing the rotation of magnetization ofthe pinned layer characteristically shows a feature that the directionof magnetization and the direction of easy axis of magnetization aredifferent in the pinned layer 34.

In the present embodiment, it is also possible to conduct the process ofthe step 4 of FIG. 7 in plural times each with a reduced duration forthe thermal annealing process.

[SECOND EMBODIMENT]

FIG. 9 shows a fabrication process of the spin valve magnetic sensor 30according to a second embodiment of the present invention, wherein thoseparts corresponding to the parts described previously are designated bythe same reference numerals and the description thereof will be omitted.It should be noted that the magnetic sensor 30 itself has a constructiondescribed already with reference to FIG. 6.

Referring to FIG. 9, the spin valve magnetic sensor 30 is subjected,after the process of the steps 1-3 corresponding to the steps 1-3 ofFIG. 7, a thermal annealing process which is conducted in a high vacuumenvironment at 210° C. under the existence of an external magneticfield, wherein the direction of the external magnetic field is set suchthat the magnetization of the pinned layer 34 intersectsperpendicularly, after the step 4 of FIG. 9, to the initial 0° directionof magnetization in the step 3.

As explained already, the angle that the magnetization of the pinnedlayer 34 forms with the initial 0° direction of magnetization becomessmaller than 90° when the direction of the external magnetic field isset perpendicularly to the foregoing initial direction of magnetization.Thus, in order to achieve the foregoing 90° angle for the magnetizationof the pinned layer 34 from the 0° direction, the present embodimentsets an offset angle in the direction of the external magnetic fieldsuch that the external magnetic field forms an angle larger than 90°with respect to the initial direction of magnetization.

FIG. 10A shows the relationship between the direction of the externalmagnetic field in the step 4 of FIG. 9 and the actual direction ofmagnetization of the pinned layer 34, wherein FIG. 10A shows the resultfor the case in which the external magnetic field has an intensity of1.5 kOe and the thermal annealing process is continued for 3 hours.

Referring to FIG. 10A, the desired perpendicular intersection of themagnetization of the pinned layer 34 with respect to the initialdirection of magnetization is achieved successfully, when the thermalannealing process is conducted at 210° C., by setting the angle of theexternal magnetic field to about 115°, which is about 25° larger thanthe nominal 90° angle. When the thermal annealing process is conductedat 230° C., this offset angle is reduced to about 10°.

Thus, it is possible to reduce the offset angle of the external magneticfield by increasing the temperature of the thermal annealing process.However, such an increase of the thermal annealing process applied tothe magnetic head 10, in which the magnetic sensor 30 is included, tendsto induce a deterioration in the magnetization of the magnetic shieldlayers 12 and 16 or in the magnetization of the magnetic pole 21, asexplained already. Thus, in order to avoid such adversary problems, itis preferable to conduct the thermal annealing process at thetemperature lower than about 210° C., in which no substantial rotationoccurs in the easy axis of magnetization of the free layer 32.

FIG. 10B shows the rotation of magnetization of the pinned layer 34 inthe step 4 of FIG. 9 for the case in which the duration of the thermalannealing process is changed.

Referring to FIG. 9B, it can be seen that the rotational angle increasesgenerally with the duration of thermal annealing process up to about 3hours. This in turn means that the duration of the thermal annealingprocess may be reduced by setting the offset angle of the externalmagnetic field somewhat larger in the step 4 of FIG. 5.

In the present embodiment, as well as in the previous embodiment, thethicknesses and compositions of the free layers 32a and 32b,non-magnetic layer 33, pinned layer 34 and the pinning layer 35 are notlimited to those described previously but other thicknesses and othercompositions may also be used. Particularly, the pinning layer 35 may beformed of a material other than PdPtMn such as NiMn, PtMn, PdMn, IrMn,RhMn and an alloy thereof.

Further, the present invention is by no means limited to thoseembodiments described heretofore, but various variations andmodifications may be made without departing from the scope of theinvention.

What is claimed is:
 1. A spin-valve magnetic head, comprising:a firstferromagnetic layer having a first easy axis of magnetization extendingin a first direction; a second ferromagnetic layer provided on saidfirst ferromagnetic layer with a separation therefrom, said secondferromagnetic layer having a magnetization in a second directionsubstantially perpendicular to said first direction, said magnetizationdefining a line of magnetization extending in said second direction; andan anti-ferromagnetic layer provided on said second ferromagnetic layerin exchange coupling therewith; said second ferromagnetic layer having asecond easy axis of magnetization extending in a direction intersectingsaid line extending in said second direction.
 2. A spin-valve magnetichead as claimed in claim 1, wherein said second easy axis ofmagnetization extends in a direction oblique to said second direction.3. A spin-valve magnetic head as claimed in claim 1, wherein saidanti-ferromagnetic layer is formed of a material that is selected from agroup consisting of NiMn, PtMn, PdMn, IrMn, RhMn, and an alloy thereof.